Submarine depth ratings

Depth ratings are primary design parameters and measures of a submarine's ability to operate underwater. The depths to which submarines can dive are limited by the strengths of their hulls.

Human occupants of a submarine would suffer physiological problems if the air pressure inside were simply allowed to be equal to the water pressure outside the hull (for example, oxygen becomes toxic at high pressures). So, when the inside air is kept at normal atmospheric pressure, the hull must be able to withstand the forces created by the outside water pressure being greater than the inside air pressure. The outside water pressure increases with depth and so the stresses on the hull also increase with depth. Each 10 metres (33 feet) of depth puts another atmosphere (1 bar, 14.7 psi, 100 kPa) of pressure on the hull, so at 300 metres (1,000 feet), the hull is withstanding thirty atmospheres (30 bar, 441 psi, 3,000 kPa) of water pressure.